﻿<p><em>IfcMaterialDefinition</em> is a general supertype for all
material related information items in IFC that have common
material related properties that may include association of
material with some shape parameters or assignments to identified
parts of a component.</p>
<p>There are three ways of assigning materials to a single component or
multiple components; they are characterized as:</p>
<ul>
<li>by layer - assigning a material to a layer with constant
thickness</li>
<li>by profile - assigning a material to a profile with a
constant of varying shape along an extrusion</li>
<li>by constituents - assigning a material to an identified part
of a component shape; the identification is by a keyword rather than 
by a shape parameter</li>
</ul>
<p>Each instantiable subtype of <em>IfcMaterialDefinition</em> may
have material properties assigned, or have an external
classification of its definition. It can be assigned to either a
subtype of <em>IfcElement</em>, or a subtype of
<em>IfcElementType</em> by using the objectified relationship
<em>IfcRelAssociatesMaterial</em>.</p>

<blockquote class="history">
HISTORY  New entity in IFC4
</blockquote>